This invention relates to improved process for reacting components such as tin tetrachloride and water vapor to form an optically-acceptable, haze-free coating on a hot glass surface. The invention also provides apparatus for carrying out the improved process and other such coating processes on hot substrates.
In chemical deposition of coatings on glass, it is very important to avoid premature reaction of the chemicals. Such premature reaction will often result in powder deposition on the coating apparatus, haze on the glass product and other such problems. Thus, it is necessary to carefully control the reaction time of such chemicals, where and when they are contacted with one another in relation to the glass and to the reactant-delivery system. Also, of course, the distribution of the reactant across the glass to be coated is important if one is to achieve the desired uniformity of the coating. In some applications, such accuracy is required down to very small fractions of a micron in coating thickness. Finally, it is desirable to provide coating apparatus which can be readily repaired if, through some accident, the apparatus is damaged or contaminated by the premature deposition of reaction product. All of these benefits must be achieved without unduly compromising the coating deposition rate. This is especially true of the very-thin coatings which make it possible to coat glass as it moves along a continuous production line, e.g. a float glass line.
U.S. Pat. No. 4,329,379 is representative of prior art attempts to provide tin oxide-coating processes utilizing the tin chloride/water vapor reaction procedures. One drawback of that design is that it wastes about one-third of the potential coating area. Another proposed design is that known as the Batelle/SIV coater wherein the reactants are fed through separate very narrow slots. It is more efficient than the design of U.S. Pat. No. 4,329,379 with respect to covering glass area. However, this Batelle design is not believed to be practical for continuous coating of wide glass sheets, say sheets 6-10 feet wide. One reason for this problem is the cost and difficulty maintaining the desired coating tolerances while regulating reactant feed through thin, reactant-feeder slots. Moreover, the effective coating zone is very short when utilizing such slot-moderated, reactant-feed procedures.